In certain designs, electric machines in the form of electric motors and/or power generators, for example, in drives of motor vehicles, have a stator with a soft-magnetic core and, wound in them or between them, they have windings made of copper wire or copper rods as well as a rotor that is arranged rotatably therein. When the windings are energized, in addition to converting electric energy into mechanical energy and vice versa, they generate thermal energy which, as a thermal load, leads to a temperature rise in the components, and this can cause damage to the electric machine and lead to a reduction in its efficiency. Particularly with hybrid drives, this can diminish the performance of the electric machine.
Therefore, among other things, cooling devices with a cooling fluid have been put forward with which the heat loss generated on the stator is dissipated by means of convection or conduction or else a combination thereof. In the simplest case, the entire electric machine is encapsulated in a housing and the cooling fluid flows around the stator and the rotor. In this context, churning losses occur at the rotating rotor so that, as is described in German patent application DE 101 22 425 A1, the cooling device, which is cooled by means of cooling fluid, is restricted to the stator. For this purpose, recesses such as flutes or grooves are provided next to each other along the stator in the housing, and they are closed off radially towards the inside by a metal sleeve as well as sealed vis-à-vis each other. The cooling medium is fed in and removed through these flutes from the outside. The production of such a cooling device is labor-intensive since an additional sleeve of a cooling jacket with external flutes has to be provided, or else the inner circumference of the housing has to be provided with such flutes.
As an alternative, a cooling jacket made of metal is inserted between the stator core and the housing, whereby the outer circumferential surface of the cooling jacket has recesses that, together with the housing, form cooling channels. The production and assembly of such cooling jackets is labor-intensive and, due to the surface roughness, small cavities that increase the heat transfer resistance are formed between the cooling jacket and the stator.